Expected: When I use disperse and it fails, I expect some kind of echo.

Actual: I have used disperse in a room with mobs without seeing an echo, without having the mobs disperse, but having a cooldown start on disperse (which I am assuming is a failure). There are still failures stating "You lost your concentration.", but those are a separate case.

Steps to reproduce:
1) Be in a dispersable room with other mobs
2) Call disperse, but fail.
2a) Only works on failures that do not also come with "You lost your concentration."

Repro Rate:
3/3

It isn't that Disperse failed, it is that everyone targeted made their saving throws. The reason you don't want an echo for that is the spam it would produce walking into a crowded room.